This project is concerned with the mechanism of transformation by the non-receptor tyrosine kinase v-Src. Recent findings suggest a model in which transformation by v-Src involves multiple pathways, of which some are dependent on the Ras oncoprotein, while others are Ras-independent. According to this model, activation of different pathways is dependent on different structural features of v-Src, with the SH3 and SH2 domains of v-Src and the tyrosine autophosphorylation site each required for some but not all of the signaling pathways activated by Src. It is also suggested that the cell-type specificity of transformation results from differences in the signaling pathways active in different cell-types; thus Ras function is required for transformation by v-Src in some cell types, but not in others. This project is concerned with the identification of Ras-dependent and Ras-independent pathways involved in transformation by v-Src and with the structural features of v-Src necessary for activation of these pathways. The first specific aim concerns the role of Ras in transformation by v- Src. Experiments will be carried out to determine whether activation of Ras is necessary for fusiform transformation of CEF, and if so whether it is sufficient. The structural features of v-Src necessary for Ras activation will be examined, and their role in phosphorylation of substrates that may mediate Ras activation, such as Shc, will be determined. Further experiments will be carried out to characterize the role of known or suspected Ras effectors, such as RalGDS, PI-3-kinase and Raf, in Ras-dependent transformation by v-Src. The second specific aim concerns the role of specific signaling proteins in Ras-independent transformation by v-Src. Candidates include v-Src substrates such as c-Cbl and Cas, cytoplasmic signaling proteins such as PI-3-kinase and protein kinase C, and Src-activated transcription factors such as AP-1, Myc and Stat3. Experiments will be carried out to determine whether the activation of the pathway occurs when signaling through Ras is blocked, whether it occurs in cells expressing host range mutants of v-Src, and whether activation of the pathway or protein is necessary and/or sufficient for Ras-independent transformation. The third set of specific aims concerns the identification of novel signaling proteins and pathways that may mediate transformation by v- Src. A complementation screen will be carried out to detect genes that complement transformation-defective mutants of v-Src.